Expression of Fos during sham sucrose intake in rats with central gustatory lesions

For humans and rodents, ingesting sucrose is rewarding. This experiment tested the prediction that the neural activity produced by sapid sucrose reaches reward systems via projections from the pons through the limbic system. Gastric cannulas drained ingested fluid before absorption. For 10 days, the rats alternated an hour of this sham ingestion between sucrose and water. On the final test day, half of them sham drank water and the other half 0.6 M sucrose. Thirty minutes later, the rats were killed and their brains immunohistochemically stained for Fos. The groups consisted of controls and rats with excitotoxic lesions in the gustatory thalamus (TTA), the medial (gustatory) parabrachial nucleus (PBN), or the lateral (visceral afferent) parabrachial nucleus. In controls, compared with water, sham ingesting sucrose produced significantly more Fos-positive neurons in the nucleus of the solitary tract, PBN, TTA, and gustatory cortex (GC). In the ventral forebrain, sucrose sham licking increased Fos in the bed nucleus of the stria terminalis, central nucleus of amygdala, and the shell of nucleus accumbens. Thalamic lesions blocked the sucrose effect in GC but not in the ventral forebrain. After lateral PBN lesions, the Fos distributions produced by distilled H(2)O or sucrose intake did not differ from controls. Bilateral medial PBN damage, however, eliminated the sucrose-induced Fos increase not only in the TTA and GC but also in the ventral forebrain. Thus ventral forebrain areas associated with affective responses appear to be activated directly by PBN gustatory neurons rather than via the thalamocortical taste system.     

Selective contributions of the medial preoptic nucleus to testosterone-dependant regulation of the paraventricular nucleus of the hypothalamus and the HPA axis

Previous data have consistently demonstrated an inhibitory effect of androgens on stress-induced hypothalamic-pituitary-adrenal (HPA) responses. Several brain regions may influence androgen-mediated inhibition of the HPA axis, including the medial preoptic area. To test the role of the medial preoptic nucleus (MPN) specifically, we examined in high- and low-testosterone-replaced gonadectomized rats bearing discrete bilateral lesions of the MPN basal and stress-induced indexes of HPA function, and the relative levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA in the amygdala. High testosterone replacement decreased plasma adrenocorticotropin hormone (ACTH) and paraventricular nucleus (PVN) Fos responses to restraint exposure in sham- but not in MPN-lesioned animals. AVP-, but not CRH-immunoreactivity staining in the external zone of the median eminence was increased by testosterone in sham animals, and MPN lesions blocked this increment in AVP. A similar interaction between MPN lesions and testosterone occurred on AVP mRNA levels in the medial nucleus of the amygdala. These findings support an involvement of MPN projections in mediating the AVP response to testosterone in both the medial parvocellular PVN and medial amygdala. We conclude that the MPN forms part of an integral circuit that mediates the central effects of gonadal status on neuroendocrine and central stress responses.     

Obesity-inducing amygdala lesions: examination of anterograde degeneration and retrograde transport

Small lesions centered in the posterodorsal region of the medial amygdala resulted in excessive weight gains in female rats. Unilateral lesions were nearly as effective as bilateral lesions in the first 48 h after surgery (+21 to +32 g). Assessment of lesion damage was done by both qualitative evaluation and by a quantitative grid-point counting method. The critical sites for weight gain were the intra-amygdaloid bed nucleus of the stria terminalis and the posterodorsal medial amygdaloid nucleus. Incidental damage to the overlying globus pallidus was negatively related to weight gain. The cupric silver method for demonstrating axonal degeneration was applied to brains with obesity-inducing lesions. A dense pattern of degenerating terminals was found in the lateral septum, amygdala, ventral striatum, and ventromedial hypothalamus. Degeneration in the paraventricular nucleus of the hypothalamus was scarce or absent. Small retrograde tracer injections made in either the intra-amygdaloid bed nucleus of the stria terminalis or in the posterodorsal medial amygdaloid nucleus labeled cells in the amygdala, lateral septum, and hypothalamus, reciprocating the anterograde projections from the amygdala to these areas. The data suggest that subdivisions of the posterodorsal amygdala participate in the regulation of feeding in a manner that is similar to the better-known role of this part of the brain in mediating reproductive behavior. Although topographical differences may exist within the amygdaloid and hypothalamic subdivisions regulating these two sexually dimorphic behaviors, the relays engaged by feeding-related connections and those related to reproduction are remarkably parallel.     

Effect on the plasma renin-aldosterone system of lesions to suprachiasmatic nuclei and central serotonin depletion in rats

Renin activity, angiotensin-converting enzyme activity and aldosterone concentration were measured in the plasma of 8 experimental groups of rats: I--sham operated non-treated rats, II--suprachiasmatic nuclei (SCN) lesioned non-treated: III--sham operated + furosemide (4 mg/kg i.p.), IV--SCN lesioned + furosemide, V--shams + 24-hour water deprivation: VI--SCN + 24-hour water deprivation, VII--intact rats + saline: and VIII--intact rats + p-chlorophenylalanine (pCPA, 300 mg/kg, i.p.). No significant changes in basal levels of the three parameters were found after SCN, lesions in comparison with sham operated controls. Furosemide caused a similar increase in all three parameters of both sham and SCN lesioned rats. Similar changes were observed in SCN rats 24 hours after water deprivation and in intact rats 48 hours after serotonin depletion by pCPA: suppressed renin activity together with increased aldosterone concentration. It is concluded that the central serotonergic system and SCN play a similar role in control of the renin-aldosterone system in rats under conditions of negative water-salt balance.     

Inhibition of ovulation in the rat by electrical stimulation of the lateral amygdala.

Effects of electrical stimulation of the lateral amygdaloid areas on ovulatory gonadotropin release were examined in adult Wistar female rats. Electrical stimulation was applied in rats in proestrus under ether anesthesia with square wave pulses of 0.5 ms duration and 100 Hz frequency for 30 min (30 sec on and off). Stimulation of the lateral amygdala blocked ovulation in 50% of animals when it was applied between 13:30 and 14:30 with a current of 300 muA. Stimulation of the medial amygdala under the same experimental condition was absolutely ineffective to block ovulation. Sham stimulation was also ineffective. In determining the gonadotropin concentration in serum, the stimulation into the lateral amygdala was observed to inhibit the ovulatory release of LH, FSH and prolactin. It may be said that the lateral amygdaloid area participates in the control of gonadotropin release in an inhibitory manner.     

Unilateral lesion of the nigrostriatal pathway decreases the response of GABA interneurons in the dorsal raphe nucleus to 5-HT1A receptor stimulation in the rat

This study examined the firing rate and pattern of electrophysiologically and chemically identified GABA interneurons in the dorsal raphe nucleus (DRN), and role of 5-HT_1A receptor agonist 8-OH-DPAT and the medial prefrontal cortex (mPFC) in the firing activity in rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The interneurons in rats with lesions of the SNc showed a more burst-firing, while having no change in the firing rate; the mPFC and combined mPFC and SNc lesions in rats decreased the firing rate of the interneurons and firing pattern shifted towards a more burst-firing compared to rats with sham lesions of the SNc, respectively. In rats with sham lesions of the SNc, administration of 8-OH-DPAT (1–243 μg/kg, i.v.) produced excitatory–inhibitory, excitatory and inhibitory effects in the firing rate of individual interneurons. However, when these effects were averaged over the group, 8-OH-DPAT had no significant effect on firing rate. In rats with lesions of the SNc, mPFC and the paired lesions, 8-OH-DPAT, at the same doses, inhibited all interneurons tested, respectively. Cumulative doses producing inhibition in rats with the paired lesions were higher than that of rats with lesions of the mPFC. In contrast to rats with sham lesions of the SNc, SNc lesion reduced expression of 5-HT_1A receptor on parvalbumin positive neurons in the DRN, a subpopulation of GABA interneurons. Our results indicate that the SNc and mPFC regulate the firing activity of GABA interneurons in the DRN. Furthermore, response of likely GABA interneurons to systemic administration of 8-OH-DPAT is altered by lesion of the SNc and mPFC.     

Unilateral lesion of the nigrostriatal pathway decreases the response of GABA interneurons in the dorsal raphe nucleus to 5-HT1A receptor stimulation in the rat

This study examined the firing rate and pattern of electrophysiologically and chemically identified GABA interneurons in the dorsal raphe nucleus (DRN), and role of 5-HT_1A receptor agonist 8-OH-DPAT and the medial prefrontal cortex (mPFC) in the firing activity in rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The interneurons in rats with lesions of the SNc showed a more burst-firing, while having no change in the firing rate; the mPFC and combined mPFC and SNc lesions in rats decreased the firing rate of the interneurons and firing pattern shifted towards a more burst-firing compared to rats with sham lesions of the SNc, respectively. In rats with sham lesions of the SNc, administration of 8-OH-DPAT (1–243 μg/kg, i.v.) produced excitatory–inhibitory, excitatory and inhibitory effects in the firing rate of individual interneurons. However, when these effects were averaged over the group, 8-OH-DPAT had no significant effect on firing rate. In rats with lesions of the SNc, mPFC and the paired lesions, 8-OH-DPAT, at the same doses, inhibited all interneurons tested, respectively. Cumulative doses producing inhibition in rats with the paired lesions were higher than that of rats with lesions of the mPFC. In contrast to rats with sham lesions of the SNc, SNc lesion reduced expression of 5-HT_1A receptor on parvalbumin positive neurons in the DRN, a subpopulation of GABA interneurons. Our results indicate that the SNc and mPFC regulate the firing activity of GABA interneurons in the DRN. Furthermore, response of likely GABA interneurons to systemic administration of 8-OH-DPAT is altered by lesion of the SNc and mPFC.     

Altered neuropathic pain behaviour in a rat model of depression is associated with changes in inflammatory gene expression in the amygdala

The association between chronic pain and depression is widely recognized, the comorbidity of which leads to a heavier disease burden, increased disability and poor treatment response. This study examined nociceptive responding to mechanical and thermal stimuli prior to and following L5‐L6 spinal nerve ligation (SNL), a model of neuropathic pain, in the olfactory bulbectomized (OB) rat model of depression. Associated changes in the expression of genes encoding for markers of glial activation and cytokines were subsequently examined in the amygdala, a key brain region for the modulation of emotion and pain. The OB rats exhibited mechanical and cold allodynia, but not heat hyperalgesia, when compared with sham‐operated counterparts. Spinal nerve ligation induced characteristic mechanical and cold allodynia in the ipsilateral hindpaw of both sham and OB rats. The OB rats exhibited a reduced latency and number of responses to an innocuous cold stimulus following SNL, an effect positively correlated with interleukin (IL)‐6 and IL‐10 mRNA expression in the amygdala, respectively. Spinal nerve ligation reduced IL‐6 and increased IL‐10 expression in the amygdala of sham rats. The expression of CD11b (cluster of differentiation molecule 11b) and GFAP (glial fibrillary acidic protein), indicative of microglial and astrocyte activation, and IL‐1β in the amygdala was enhanced in OB animals when compared with sham counterparts, an effect not observed following SNL. This study shows that neuropathic pain‐related responding to an innocuous cold stimulus is altered in an animal model of depression, effects accompanied by changes in the expression of neuroinflammatory genes in the amygdala .     

Implantation of dihydrotestosterone propionate into the lateral septum or medial amygdala facilitates copulation in castrated male rats given estradiol systemically

Two experiments were conducted to determine whether unilateral implantation of dihydrotestosterone propionate (DHTP) into different brain regions of castrated rats, bearing silastic capsules containing estradiol, could augment sexual behavior without appreciable leakage of androgen into the peripheral circulation. In Experiment 1 implanation of pulverized crystalline DHTP (via 25-gauge, 1-mm-long pellets) facilitated mating significantly without stimulating penile spine growth, provided the pellets were positioned in the lateral septum or medial amygdala. Insertion of DHTP pellets into the preoptic area-anterior hypothalamus, caudate-putamen, or the border of the substantia nigra and ventral tegmental nucleus or of cholesterol pellets into lateral septum or medial amygdala had no behavioral effects. Implanation of DHTP into the lateral septum also failed to activate penile erections in rats restrained in a supine position. In Experiment 2 implantation of different bone wax dilutions of DHTP (via 25-gauge, 1-mm-long pellets) into the preoptic area-anterior hypothalamus augmented males' sexual performance only in that group in which penile spine growth was also significantly stimulated. The results sugggst that 5α-reduced androgen is capable of activating mating in the male rat by acting locally in the lateral septum and/ or medial amygdala.     

Immunohistochemical analysis of splenic tissue in rats with destruction of the hypothalamic structures

The immunoenzyme histochemical technique to stain the IgM- and IgD-bearing cells was used to study the morphometric characteristics of B-lymphocyte-dependent zones in spleen white pulp of Wistar rats (intact, sham operated and after cortex or hypothalamic lesions). In the groups of sham-operated and cortex-lesioned rats it has been shown the increase of spleen weight 7 days after the operation due to the increase of the red pulp weight. The white pulp compartment's ratio is not affected. Lesioning of the posterior hypothalamic area prevents these effects of the operation, while local coagulation of the lateral hypothalamic area causes a significant decrease of the weight of spleen primary follicules which contain IgM+IgD+-bearing B-lymphocytes exerting characteristics of circulating pool of B-lymphocytes. These data are in favour of the CNS participation in regulation of B-lymphocyte migratory activity.     

Influence of the medial raphe nucleus damage on discharge activity of the central and bazolateral nuclei of the amygdala

It has been revealed pronounced differences between neuronal discharge activity of central and basolateral nuclei of amygdala. After midbrain raphe medial nucleus damage discharge activity of amygdalar nuclei markedly changes, mainly by reciprocal manner. It is suggest that serotonergic afferentations from nucleus raphe to show various influence upon discharge activity of central and lateral nuclei of amygdala.     

Role of septum and preoptic area in regulating masculine and feminine sexual behavior in male rats

The effects of septal or preoptic lesions on both masculine and feminine sexual behaviors were examined in castrated adult male rats. Three weeks after brain surgery, animals were implanted with Silastic tubes containing testosterone (T) and observations of masculine sexual behavior were carried out four times every 5 days. T tubes were removed immediately after the end of the masculine behavioral tests. Two weeks later, animals implanted with Silastic tubes containing estradiol-17 beta(E2) were subjected to three feminine sexual behavioral tests at 5-day intervals. The bilateral lateral septal lesion (LSL) and the medial preoptic lesion (MPOL) effectively suppressed the performance of mounts, intromissions, and ejaculations, whereas the medial septal lesion (MSL), the dorsolateral preoptic lesion (DPOL), and the sham operation did not show any significant suppression of these behaviors. In the feminine sexual behavioral tests, intact and sham-operated control males showed only a low lordotic activity. However, the performance of the lordosis reflex was markedly facilitated by LSL or DPOL, while the lordotic activity of MSL and MPOL males was not significantly different from that of control males. These results suggest that the lateral septum exerts not only a facilitatory influence on masculine sexual behavior but also an inhibitory influence on feminine sexual behavior in male rats. On the other hand, the medial preoptic area may play a critical role in regulating masculine sexual behavior in male rats.     

Variations in hoarding behavior following regional hippocampal lesions in rats

Instinctual behaviors of feeding (food intake) and hoarding (HS) so also the body weight and estrus cycles (EI) were studied before and after discrete bilateral electrolytic lesions of dorsal hippocampus in female rats. Following the lesions, there was significant increase in food intake, body weight, hoarding score and disruption of 4-5 days estrus cycles with EI of more than one, as compared to the control (prelesioned) period and the sham operated rats. Lesions of ventral hippocampus in the earlier study (Indian J exp Biol, 26 (1988) 53) had shown a significant decrease in hoarding thus suggesting a differential role of the hippocampus probably mediated through the amygdala and/or hypothalamus both of which either alone or together exert a more direct and pivotal control in the feeding and hoarding behaviour.     

Celecoxib after the onset of reperfusion reduces apoptosis in the amygdala

Reperfused myocardial infarction induces an inflammatory response that is responsible for local and systemic alterations. Among these, apoptosis observed in the amygdala following myocardial infarction has been pointed out as a consequence of such an inflammatory process. We hypothesized that inhibition of the inducible inflammatory enzyme Cox-2 during the reperfusion period may attenuate the apoptotic process in the amygdala. Anaesthetized rats were subjected to left anterior descending coronary artery occlusion for 40 min, followed by reperfusion. The Cox-2 antagonist Celecoxib (3 mg/kg i.p.) was administered 10 min after the onset of the reperfusion period. After 72 h of reperfusion, infarct size was determined and the lateral and medial amygdala were dissected from the brain. Infarct size was similar between untreated and Celecoxib-treated animals (40–45% of the area at risk). Cox-2 expression was significantly reduced in both parts of the amygdala in the Celecoxib group. Apoptosis regression was observed in the amygdala of the Celecoxib group as shown by decreased number of TUNEL positive cells and by decreased of caspase-3 activation. Bax/Bcl-2 ratio was not significantly altered by Celecoxib while Akt activation was increased in the lateral amygdala but not in the medial amygdala. This data indicates that inhibition of Cox-2 by Celecoxib is associated with regression of apoptosis in the amygdala following myocardial infarction.     

Combination unilateral amygdaloid and ventromedial hypothalamic lesions: evidence for a feeding pathway

Previous studies have reported hyperphagia and obesity in female rats with bilateral lesions of the most posterodorsal part of the amygdala. In rats with unilateral posterodorsal amygdaloid lesions, a dense pattern of anterograde degeneration appears in the ipsilateral ventromedial hypothalamus, but not the contralateral nucleus. In the present study, female rats with unilateral ventromedial hypothalamic lesions or sham lesions were given either sham lesions or unilateral lesions of the posterodorsal amygdala (PDA) 20 days later. Unilateral lesions of the ventromedial hypothalamus resulted in hyperphagia and excessive weight gain. Subsequent amygdaloid lesions that were contralateral to the initial hypothalamic lesions resulted in hyperphagia and additional excessive weight gains, but amygdaloid lesions ipsilateral to the initial hypothalamic lesions did not. It is concluded that the effects of the two lesions on body weight are not additive and that the PDA and ventromedial hypothalamus are part of the same ipsilateral pathway regulating feeding behavior and body weight regulation.     

Candidates for the light entrainment pathway to the circadian clock of the Madeira cockroach Rhyparobia maderae

The circadian pacemaker controlling locomotor activity rhythms in the Madeira cockroach is located at the accessory medulla (AMe). The ipsi- and contralateral compound eyes provide light input to the AMe, possibly via the γ-aminobutyric acid (GABA)-immunoreactive (-ir) distal tract, which connects the glomeruli of the AMe to the ipsilateral medulla and lamina. To identify possible light-entrainment pathways, double-label immunocytochemistry was performed employing antibodies against GABA, myoinhibitory peptide (MIP), allatotropin (AT) and orcokinin (ORC). While all antisera tested, except the anti-ORC, prominently stained the glomeruli of the AMe, colocalization with anti-GABA was detected neither in the glomeruli nor in the distal tract. However, one median neuron that colocalized GABA-, AT- and MIP-immunoreactivity appeared to connect all glomeruli of the AMe to the medulla and lamina. Furthermore, one distal–frontoventral local neuron with arborizations in all glomeruli of the AMe colocalized anti-AT- and anti-MIP immunoreactivity. As candidates for contralateral light entrainment pathways, one ventromedian and one ventral neuron colocalized MIP- and ORC immunoreactivity, projecting via posterior and anterior commissures. Both branched in the interglomerular region of the AMe, where arborizations co-labeled with anti-ORC- and anti-MIP antisera. A possible role for MIP in light entrainment is supported also by injections of Rhyparobia maderae-specific MIP-2, which generated an all-advance phase-response curve late at night. Future experiments will challenge our hypothesis that GABA-, MIP- and AT-ir neurons provide ipsilateral light entrainment to all glomeruli, while MIP- and ORC-ir neurons carry contralateral light entrainment to the AMe’s interglomerular region, either delaying or advancing AMe neurons light-dependently.     

Effects of lesions in the medial preoptic region on precocial copulation in the male chick

Chicks showing androgen-induced precocial copulation to a prone hand were given bilateral electrolytic lesions in the medial preoptic region. Symmetrical lesions in the medial preoptic area disrupted copulatory behavior over the 10-day postoperative test period. Asymmetrical or sham lesions did not differentially affect copulatory activity. Postoperative records indicated that all animals showed similar increases in weight gain and comb size.     

The distribution pattern of alpha-MSH-like immunoreactivity in the cat central nervous system

The distribution pattern of alpha-melanocyte stimulating hormone-like immunoreactivity (alpha-MSH-Li) was studied in cats using avidin-biotin modification of immunocytochemical method. Cell bodies containing alpha-MSH-Li were observed in the medial basal hypothalamus, especially in the infundibular nucleus, the lateral hypothalamus and near zona incerta. Fibers with alpha-MSH-Li extended beyond the hypothalamus, into the paraventricular nucleus of the thalamus, rostral amygdala, periaqueductal gray, locus ceruleus, parabrachial nucleus and medial nucleus of the nucleus tractus solitarius. Axons with alpha-MSH-Li were also seen diffusely in various cortical areas, but more extensively in the limbic cortical regions. The distribution pattern of the cell bodies and fibers containing alpha-MSH-Li bears several similarities to that seen in rats, but differs in that the alpha-MSH-Li was not observed in cell bodies in locations other than the medial basal and lateral hypothalamus.     

Neural Basis of Anticipatory Anxiety Reappraisals

Reappraisal is a well-known emotion regulation strategy. Recent neuroimaging studies suggest that reappraisal recruits both medial and lateral prefrontal brain regions. However, few studies have investigated neural representation of reappraisals associated with anticipatory anxiety, and the specific nature of the brain activity underlying this process remains unclear. We used functional magnetic resonance imaging (fMRI) to investigate neural activity associated with reappraisals of transient anticipatory anxiety. Although transient anxiety activated mainly subcortical regions, reappraisals targeting the anxiety were associated with increased activity in the medial and lateral prefrontal regions (including the orbitofrontal and anterior cingulate cortices). Reappraisal decreased fear circuit activity (including the amygdala and thalamus). Correlational analysis demonstrated that reductions in subjective anxiety associated with reappraisal were correlated with orbitofrontal and anterior cingulate cortex activation. Reappraisal recruits medial and lateral prefrontal regions; particularly the orbitofrontal and anterior cingulate cortices are associated with successful use of this emotion regulation strategy.     

Neuronal signalling of fear memory

The learning and remembering of fearful events depends on the integrity of the amygdala, but how are fear memories represented in the activity of amygdala neurons? Here, we review recent electrophysiological studies indicating that neurons in the lateral amygdala encode aversive memories during the acquisition and extinction of Pavlovian fear conditioning. Studies that combine unit recording with brain lesions and pharmacological inactivation provide evidence that the lateral amygdala is a crucial locus of fear memory. Extinction of fear memory reduces associative plasticity in the lateral amygdala and involves the hippocampus and prefrontal cortex. Understanding the signalling of aversive memory by amygdala neurons opens new avenues for research into the neural systems that support fear behaviour.